The general objectives of the project are the continued development of a theory accounting for the way in which the behavior of organisms is modified by its rewarding and punishing consequences, with special emphasis on the role of feedback processes. The experimental program of this project is concerned especially with the way in which the general theory can be extended and applied to human behavior by relating basic mechanisms to information processing concepts. The specific objectives of the current year have had to do largely with the way in which information that an individual has stored in memory regarding event probabilities is used in the guidance of choice and decision behavior. In practical situations rewards and punishments are nearly always uncertain, and consequently selective learning, to be adaptive, depends heavily on the organism's ability to adjust its choices to conform to true probabilities of punishment and reward. Earlier work on probability learning has been somewhat isolated from the mainstream of research in human memory and information processing and consequently has not yielded the concepts needed for the interpretation of problems of reinforcement. The research program of the present year was planned to begin to overcome these deficiencies.